Rayleigh wave group velocity tomography in the Aegean area

Data from a large-scale experiment which took place in Greece during the period January-July 1997 have been used to investigate the structure of the Aegean area using surface waves. During this experiment, 30 seismic broadband instruments were deployed throughout the whole Greek area. Additional data during the period 1996-2000 from other temporary networks have been included in the dataset. One hundred eighty-five events with magnitudes 4.0:! M,:5 5.5 recorded by these stations have been collected and processed. The individual dispersion curves of the group velocity of Rayleigh waves for each source-station path have been calculated, producing more than 700 paths covering the studied region. These curves have been used to determine Rayleigh group velocity maps using a 2D-tomography method. On the basis of a regionalization of the dispersion measurements, local averaged dispersion curves have been obtained and non-linearly inverted to obtain models of shear-wave velocity versus depth. Since the dispersion curves in the period range 5 s less than or equal to T less than or equal to 30 s are mostly affected by the crustal structure, the model velocities are estimated down to a depth of approximately 35-45 km. The results from the non-linear Hedhehog inversion as applied to a few local dispersion curves show a crustal thickness of approximately 32 km for the Northern Aegean Sea, and a relatively thin crust of approximately 22-24 km for the Southern Aegean Sea. (C) 2002 Elsevier Science B.V. All rights reserved.